add margins to drop area to make it easier to drop buttons on the title bar (fixing 346222)

change cursor to a non-pointing one [1]

[1] Drag&drop: When dropping, we receive the position of the button being dropped,
not of the cursor. The two can be far (when starting drag by moving the cursor fast):
which makes the whole experience very confusing, as the user means to drop at cursor location.

Test Plan: Tested drag/drop: same (messy) behavior as before, but can now drop more loosely around titlebar items